This invention relates generally to air conditioning and more particularly to an air-cycle, air conditioning system incorporating evaporative cooling apparatus.
Air conditioning systems for vehicles are basically two types. One is the closed-loop, vapor cycle which is commonly used in automobiles. This type of system is undesirable for use in an aircraft because of high component weight and substantial power requirements which may, in some cases, produce unsafe conditions. The other is the air-cycle, air conditioning system which has been recognized by the art as the preferred aircraft air conditioning system.
An air-cycle, air conditioning system is generally comprised of a compressor, an air-to-air heat exchanger, and an expansion cooling turbine; all of which are series interconnected. The heat exchanger includes two flow paths one of which is arranged to received compressed air from the compressor and the other is arranged to receive ram air(i.e., atmospheric air compressed by the forward motion of the aircraft). The purpose of the ram air is to withdraw heat given up to the heat exchanger by the compressed air. The turbine then further cools the compressed air and finally discharges it into the enclosure of the aircraft substantially reduced in both temprature and pressure.
A problem associated with employing ram air as a heat exchanger coolant is that at high aircraft speeds skin friction causes significant increases in the immediate air temperature. The hotter air is a poorer heat sink to the air being conditioned in the heat exchanger. However loss of an adequate heat sink for the system can be offset by impinging condensate extracted from the system upon the heat exchanger thereby effectuating evaporative cooling. Similarly, a further problem of aircraft drag attributable to the quantity of ram air that must be ingested to provide heat sinking is likewise alleviated by auxiliary evaporative cooling.
U.S. Pat. No. 4,018,060 issued to Kinsell et al. discloses an air-cycle, air conditioning system incorporating auxiliary evaporative cooling apparatus to impinge extracted condensate on a heat exchanger. A power source, which is independent of the air conditioning system, transports and disperses extracted condensate by creating a pressure differential between the point of condensate extraction and the point of condensate dispersion. A disadvantage in relying on an independent power source is that any impairment in the power source likewise adversely affects the apparatus' ability to provide evpaorative cooling. Also, small breaks or openings along the condensate's transportation path would decrease the pressure differential, and thus the transporting capability.